The Orthogonal Frequency Division Multiple Access (OFDMA) technology adopted in the traditional Long Term Evolution (LTE) system is designed based on a basic idea of orthogonal transmission, wherein the transmitting and receiving are simple and easy to realize, and the performance can also be ensured. However, along with the rapid development of the applications of the services of mobile internet and internet of things, owing to its greater advantages in improving system capacity, reducing time delay and supporting more user equipments, the non-orthogonal multiple access (NOMA) technology is more likely to be adopted in a 5G mobile communication system. In the NOMA technology, information of different user equipments are superposed on a same transmission resource for transmission, thereby artificially introducing interference which needs to be eliminated through a more complex receiver algorithm at a receiving end. At present, some typical NOMA technologies mainly include the Non-Orthogonal Multiple Access (NOMA), the Sparse Code Multiple Access (SCMA), and the Pattern Division Multiple Access (PDMA), etc.
By adopting the NOMA technology, signals of multiple user equipments can be superposed at a power domain, and a successive interference cancellation receiver is adopted at a receiving end. SCMA is a novel frequency domain non-orthogonal multiple access technology, wherein different data streams are mapped onto different code words of a multidimensional codebook, each code word represents an extensible transport layer, and all the SCMA transport layers share the same time-frequency resource. A receiving end can decode by adopting an iterative message passing algorithm (MPA) and utilizing the sparsity feature of code words, with the performance approximating the performance obtained through optimal detection. In the PDMA technology, by utilizing a pattern division technology and based on the non-orthogonal feature patterns of multiple signal domains including power domain, code domain and space domain of the user equipment signals, user equipments are distinguished at the transmitting end. At the receiving end, based on a characteristic structure of a pattern of the user equipment, multi-user equipment detection is realized by adopting a successive interference cancellation method, which can approximate a capacity bound of a multiple access channel.
In the existing PDMA technology, an encoding matrix can be used as a basic mapping pattern to distinguish multiple user equipments. Generally, a row of an encoding matrix corresponds to a group of frequency resources participating in data mapping multiplexed by multiple user equipments, and a column represents a pattern mapping manner of a multi-user equipment data. For example, each column of an encoding matrix is used by a user equipment, while the maximum number of multi-user equipments supported by PDMA is the total number of columns of an encoding matrix. Alternatively, multiple columns of an encoding matrix can also be used by a same user equipment.
If each column of an encoding matrix of PDMA corresponds to a layer of data stream, when multiple layers of data streams (data of a same user equipment or data of different user equipments) reach the receiving end (a base station in uplink or a user equipment in downlink) via a same channel, multiple layers of data streams use the same modulation constellation and the same power at present, which is disadvantageous for signal detection (e.g., using a Belief Propagation (BP) algorithm) at the receiving end due to the fact that corresponding modulation constellation diagrams are superposed when multiple layers of data modulation symbols reach the receiving end via a same channel.
In conclusion, each column of an encoding matrix of PDMA corresponds to a layer of data stream, and multiple data streams use the same modulation constellation and the same power, which is disadvantageous for signal detection at the receiving end due to the fact that corresponding modulation constellation diagrams are superposed when multiple layers of data modulation symbols reach the receiving end via a same channel.